Originally posted by Fzanco:

That's an assumption as a full biome load has not happened yet and may actually differ from loading in new poi's. this is going to be a much larger change and may require a different approach to generation. I don't know programming, but saying something as fact when the evidence presented only gives an educated guess is a bit

Here's from the FAQ of their official discord:
Will new content be added to my world I currently are playing on?
New content such as tar pits, mountain caves and Mistlands in the future will not appear in areas that have been already generated. Areas are generated 300-500 meters from a player's location. Exploremap and resetmap has no effect.